The present invention relates to a sighting device at a firearm, more particularly at a launcher, for adjusting the elevation of same, with an annular vessel system surrounding the tube of the arm, in which a surface of a liquid indicates the elevation. A known liquid sighting device of this type comprises two diametrically opposite spaces extending in parallel to the axis of the tube of the arm, in each of which a column of liquid is present and these axially extending spaces are connected at the top and at the bottom by two lateral annular spaces (communicating vessels). In one of the axially extending spaces the column of liquid is visible through a window and it shows the elevation which can be read on a scale provided on the window as illustrated in U.S. Pat. No. 4,466,197 to Staempfli (corresponding to Swiss Patent Application (CH-PS No. 637 765). Tests have shown that in some applications this known sighting device has not the required precision. The known liquid sighting device comprises a relatively great volume of liquid for a relatively small free surface of the liquid so that the dilatation of the liquid when heated behaves like in a thermometer and the indication is considerably altered.
A similar slant angle indicator with a cylindrical container of annular section is shown from PATENT ABSTRACTS OF JAPAN, Vol. 10, No. 157, JP-A No. 61 11 609. The container is partly filled with a conductive liquid and the wall of the container is provided with sensors which are influenced by the liquid and which are connected to a processor which determines the slant in two dimensions. This slant angle indicator is too expensive for relatively simple firearms. Moreover, also in this case, the volume of liquid versus the free surface of the liquid is considerable as well as the dependence on temperature.
Further, a sighting device is known from EP-A No. 0 190 549 which comprises at the side of the tube of the arm, in a plane parallel to the axis of the tube, an annular container which is filled about up to one half with a liquid. A scale at the periphery of the container permits to read the elevation. Also in this case, the volume of the liquid versus the free surface of the liquid is considerable as well as the dependence on the temperature.